This invention relates to an improved heat pump that is integrated with a domestic hot water system to provide six separate modes of operation utilizing a minimum amount of additional equipment.
Integrated heat pump systems of this type have been used for some time to heat domestic hot water. Typically, in the earlier systems, superheated refrigerant vapors leaving the discharge end of the heat pump compressor are brought into heat transfer relation with a flow of water within a desuperheater. A portion of the energy in the refrigerant is rejected into the water thereby raising the temperature of the water. The amount of water heating provided by this type of system is limited and water heating cannot be accomplished unless the heat pump is delivering heating or cooling to a comfort region.
Robinson in U.S. Pat. No. 4,598,557 discloses an improved integrated heat pump system having a refrigerant to water heat exchanger for heat flow of water passing therethrough. Through use of a rather complex valve and piping network the vapor fan coil of the heat pump can be removed from the refrigerant flow circuit and the water to refrigerant heat exchanger selectively adapted to carry the entire condensing load. As a result, hot water can be generated when the system is not called upon to deliver either heating or cooling to the indoor comfort zone. The independent hot water mode of operation provided by Robinson represents an important step forward in the art.
Recently, U.S. Pat. No. 4,646,537 issued to Crawford describing an integrated heat pump that is capable of delivering six separate modes of operation. These include comfort zone heating and cooling with or without domestic hot water heating, hot water heating without comfort zone heating or cooling, and lastly a defrost mode in which the outdoor heat exchanger is defrosted using energy stored in the hot water side of the system. Crawford again utilizes a rather complex valving and piping network to achieve this highly desirous result which is expensive and difficult to maintain.
In both the Robinson and Crawford systems, entire sections of the system are closed off or isolated when the system mode of operation is changed. Varying amounts of refrigerant are thus trapped in the isolated sections seriously effecting the actual amount of refrigerant that might be available during any operational mode. This of course creates serious refrigeration management problems that are difficult to overcome. Furthermore, because of the number of valves that must be cycled during each mode change, the control equipment required to regulate the system is also correspondingly complex and expensive.
In co-pending application Ser. No. 017,167 filed Feb. 20, 1987, U.S. Pat. No. 4,727,727, in the name of Reedy which is assigned to the present assignee, there is disclosed an integrated heat pump system which like Crawford can selectively deliver six separate modes of operation. However, unlike Crawford, this improved system can achieve mode changes employing only two additional control valves and a minimum amount of additional piping. In the improved system, all the refrigerant flow sections are arranged so that they are always exposed to the inlet side of the heat pump compressor regardless of the mode of operation that is being used. As a result, the refrigerant in any unused section is drawn into the compressor and rerouted through the active sections thus providing for total utilization of the refrigerant and thus avoiding the refrigerant management problems found in other similar type systems.
As will be explained in greater detail below, the present integrated heat pump improves upon Reedy by further eliminating unnecessary valves and piping circuits without sacrificing any of the advantages found in Reedy.